1. Field of the Invention
This invention relates to an apparatus for treating fluids and more particularly but not solely to an apparatus for disinfecting water.
2. Related Background Art
It is well known that high-intensity ultra-violet (UV) light has germicidal properties which can be used to sterilize water. EP-A-0202891 discloses a fluid treatment apparatus which utilizes these germicidal properties, and which comprises an elongate tubular duct having inlet and outlet ports at or adjacent its opposite ends, an elongate UV light source extending along the axis of the duct and a guide vane extending helically along the internal wall of the duct between the input and output ports.
Water treatment companies are reluctant to utilize UV sterilizers of the above-mentioned type because they do not effectively treat all of the water. One reason for this is that slime and other matter, which accumulates on the surface of the lamp submerged in the water, attenuates the UV light so much that micro-organisms which do not come within close proximity of the UV lamp do not receive a dose of UV radiation which is sufficient to kill them. Furthermore, the main accumulation on the lamp is attributable to the dead carcasses of micro-organisms: such carcasses undesirably act to filter a substantial amount of the UV light being transmitted.
In order to overcome the above-mentioned problems, fluid treatment apparatus are known which comprise a sleeve of polytetrafluoroethylene (PTFE), mounted as close but sliding fit on the elongate lamp. A piston can be actuated to occasionally drive the sleeve along the lamp, so as to clean the latter.
A disadvantage of this arrangement is that the sleeve actually smears the slime and other debris and in fact exacerbates the problem.
Another disadvantage of this arrangement is that the lamp may be slightly irregular in cross-section and thus there is a risk that the sleeve could miss the lamp, with the result that the lamp may not cleaned in some areas. There is also a risk that the sleeve could foul and break the lamp.
We have now devised a fluid treatment apparatus which alleviates the above-mentioned problems.